Method for transmitting prioritized data and a transmitter

ABSTRACT

Described is a method for transmitting continuously created data items from an aircraft to a receiver. The data items are of a plurality of data types and each have a different priority. For each data type a live LIFO buffer and a main LIFO buffer are provided. In a regular operation mode continuously created data items are continuously stored in the main buffers. In a transmission operation mode continuously created data items are continuously stored in the live buffers, consecutive data packets are transmitted and for each data packet the data is selected from the buffers, wherein data items stored in live buffers are transmitted before data items stored in main buffers and data items of higher priorities are transmitted before data items of lower priorities. Further, a transmitter and an aircraft are described and claimed.

FIELD OF THE INVENTION

The present invention relates to a method for transmitting continuouslycreated data items from an aircraft to a receiver, a transmitter fortransmitting continuously created data items from an aircraft to areceiver and an aircraft comprising such a transmitter.

BACKGROUND OF THE INVENTION

Today flight accident investigations largely rely on the data recordedin the so-called flight recorder. Flight recorders used onboardcommercial aircraft are usually fixed to the aircraft. Thus, if accessto the aircraft itself is difficult, for example, because the aircraftaccident occurred over open water and the wreckage sunk after theaccident, it may be difficult to retrieve the flight recorder. Toovercome this disadvantage, it has been suggested to transmit at leastpart of the data stored in the flight recorder from an aircraft to areceiver, e.g., a ground station before the accident happens such thatat least some information is readily available well before the flightrecorder has been successfully retrieved.

BRIEF SUMMARY OF THE INVENTION

In the prior art it has been suggested to continuously transmit the datastored in the flight recorder from the aircraft to a ground station. Dueto the high cost of satellite data transmission and the limitedbandwidth available, this approach is not feasible in practice, inparticular, as most of the transmitted data is not required and would bediscarded immediately. It has, therefore, previously been suggested totransmit flight recorder data only after it has been detected that anaccident is likely to occur. While this approach prevents extensivecosts due to unnecessary data transmission, the bandwidth and thetransmission time available will usually be limited. Thus, a choice hasto be made which kind of the flight recorder data is transmitted fromthe aircraft to a ground station.

It is, therefore, an aspect of the present invention to provide a methodand a transmitter for selectively transmitting flight recorder data froman aircraft to a receiver before an aircraft accident takes place thattakes into consideration that various types of data may be transmittedand that the transmission time and bandwidth are limited.

In a first aspect the problem is solved by a method for transmittingcontinuously created data items from an aircraft to a receiver. The dataitems are of a plurality of data types and each of the plurality of datatypes is assigned a different priority ranging from a highest priorityto a lowest priority. Last-in-first-out buffers are provided for storageof the continuously created data items. For each data type a separatelive buffer and a separate main buffer are provided and associated withthe respective data type. Data items of a specific data type are onlystored in the associated buffers. In a regular operation modecontinuously created data items of the plurality of data types arecontinuously stored in the associated main buffers. In a transmissionoperation mode

-   -   continuously created data items of the plurality of data types        are continuously stored in the associated live buffers,    -   consecutive data packets are transmitted from the aircraft to a        receiver via a data transmission link, each data packet        comprising a header section and a payload section, and    -   for each data packet the data to be transmitted in the payload        section is selected from the buffers, wherein any data item        stored in a live buffer is transmitted before any data item        stored in a main buffer, wherein of those data items stored in        one of the live buffers, any data item of a data type having a        higher priority is transmitted before any data item of a data        type having a lower priority, and wherein of those data items        stored in one of the main buffers, any data item of a data type        having a higher priority is transmitted before any data item of        a data type having a lower priority.

In other words, the method according to an aspect of the presentinvention transmits continuously created data items of different datatypes with different priorities. Within the present application, theterm “continuously” does not necessarily refer to data items that arecreated non-intermittently, i.e., there may even be longer gaps in timebetween the two consecutive continuously created data items. The term“continuously” describes that the data items are created over the entiretime of a flight whenever scheduled or whenever an event occurs that isreflected in a data item. Continuously created data items have to beseen in contrast to data items of fixed content, such as, for example,an identifier of an aircraft.

A data item may be any kind of grouped information that is intended forstorage in a flight recorder or for transmission with the methodaccording to an aspect of the present invention. Thus, a data item inits broadest form is a set of bits of different length and differentcontent. The length of the bit stream and the content depends on thedata type. Examples of data types are flight data, air traffic controlmessages, cockpit voice recordings and cockpit images. Flight data maycomprise, for example, recordings of a course of an aircraft, analtitude of the aircraft, a roll rate, a yaw rate and control inputs ofpilots. Air traffic control messages are data messages received by anaircraft and may, for example, include flight plans, meteorological dataor notice to airmen. Cockpit voice recordings may, for example, includeany oral communication of pilots via radio or any word spoken in thecockpit of the aircraft. Finally, cockpit images can, for example, beimages captured by a camera mounted in the cockpit of an aircraft. In anexemplary, preferred embodiment the method is adapted to transmit dataitems of the following data types: flight data, air traffic controlmessages and cockpit voice recordings.

Each data type has an assigned priority selected from a range ofpriorities ranging from a highest priority to a lowest priority. Forexample, if data items of the data types flight data, air trafficcontrol messages and cockpit voice recordings shall be transmitted, airtraffic control messages data items could be assigned the highestpriority, cockpit voice recordings data items could be assigned thelowest priority and flight data data items could be assigned anintermediate priority.

The method according to an aspect the present invention uses buffers fortemporary storage of data items. The buffers are all last-in-first-out(LIFO) buffers or stacks. Thus, data items are arranged in the buffersin the order in which they were stored in the buffer, i.e., pushed ontothe stack. In other words, the data items are stored in the buffer in atemporal order and it is only possible to retrieve the data items storedin the buffer in a temporal order. Thus, if a data item shall beretrieved from the buffer, the data item stored last is retrieved, thanthe data item stored second to last and so on. In other words, whenevera data item shall be retrieved from the stack, the data item stored lastis pushed first from the stack and reveals the data item stored secondto last and so on.

For each of the data types that shall be transmitted at least twoseparate associated buffers are provided: a live buffer and a mainbuffer. For example, if data items of the data types flight data, airtraffic control messages and cockpit voice recordings shall betransmitted with the method, a live buffer and a main buffer areprovided for flight data, a live buffer and a main buffer are providedfor air traffic control messages and a live buffer and a main buffer areprovided for cockpit voice recordings. Data items of a specific datatype can only be stored in the associated buffer, e.g., data items ofthe data type flight data can only be stored in a flight data mainbuffer or a flight data live buffer. As each live buffer and each mainbuffer is associated with a data type, each data type is also associatedwith one main buffer and one live buffer.

The method can operate in two different operation modes: a regular ornormal operation mode and a transmission operation mode. In the regularoperation mode the data items that may be transmitted according to themethod are continuously stored in the associated main buffers. In otherwords, whenever a new data item of a data type that shall be transmittedin the transmission operation mode is created, the data item is storedin the main buffer associated with the data type of the data item, i.e.,pushed on top of the stack of the main buffer of the respective datatype. No data is transmitted in the regular operation mode.

When the method switches from the regular operation mode to atransmission operation mode, continuously created data items are notstored in the main buffers associated with the respective data typesanymore, but stored in the live buffers associated with the respectivedata types. In other words, once the method has switched to atransmission operation mode, it stores any created data items in thelive buffer associated with the data type of the created data items,i.e., an air traffic control message data item received by the methodwhen it operates in the transmission operation mode is stored in the airtraffic control messages live buffer.

Further, in the transmission operation mode consecutive data packets aretransmitted from the aircraft to a receiver via a data transmissionlink. For example, data packets in form of internet protocol (IP) datapackets are transmitted via a transmission link in form of a satellitecommunication data connection to a receiver in form of a ground station.The data packets comprise a header section and a payload section. Theheader section may comprise, for example, an IP header, a user datagramprotocol (UDP) header and an aircraft identifier. In the payload sectionof the data packet, selected data from the data items stored in thebuffers is transmitted.

This data is selected according to the following rules. Any data itemstored in a live buffer is transmitted before a data item stored in amain buffer. Any data item stored in a live buffer of a data type havinga higher priority is transmitted before a data item stored in a livebuffer having a relatively lower priority. Finally, any data item storedin one of the main buffers of a data type having a higher priority istransmitted before a data item having a relatively lower priority. Forexample, if data items of the data types flight data, air trafficcontrol message and cockpit voice recordings shall be transmitted andflight data has the highest priority assigned, air traffic controlmessages an intermediate priority and cockpit voice recordings thelowest priority, any air traffic control message item stored in livebuffer is transmitted before any other data item. Next, if no more airtraffic control message data items are stored in the associated livebuffer, any flight data data item stored in a live buffer is transmittedfollowed by any cockpit voice recording data item. Finally, data itemsstored in the main buffers are transmitted in the same order. It shouldbe noted that a data item that is transmitted will be removed from therespective buffer such that the buffer comprises one data item less thanbefore.

While data packets are transmitted, new data items may be created. Suchnewly created data items are stored in the live buffers associated withthe respective data types. Every time the method selects data items forthe payload section of the next data packet to be transmitted, it firstselects data items from the live buffers in the order of the priority ofthe respective associated data types before selecting data items frommain buffers in the order of the priority of the respective associateddata types.

In the above example, when a new flight data data item is created whilethe method operates in transmission operation mode, this data item ispushed on top of the stack forming the flight data live buffer. Now whenthe method selects data items for the next data packet, the data itemstored last in the live buffer is selected first. In other words, thelatest data item of the data type having the highest priority is alwaystransmitted first. Afterwards, all other data items of the data typehaving the highest priority and received by the method after the methodhas switched into transmission operation mode are transmitted. Next, alldata items of the next lower priority received after the method hasswitched to transmission operation mode are transmitted in the oppositetemporal order in which they were created. The further data items thenfollow in the same manner. Data items stored in the main buffer, i.e.,data items received by the method before the method has switched to thetransmission operation mode are only transmitted if all data itemsreceived after the method has switched to transmission operation modehave been transmitted.

Thus, the use of LIFO buffers and the selection of data items in theorder from live buffers to main buffers and in the order of the priorityof the data type associated with the buffers advantageously ensures thatthe latest data items created or received by the method once thetransmission operation mode has been activated which have been given thehighest priority are transmitted before any other data item having alower priority or received before the transmission operation mode hasbeen activated. The method, therefore, advantageously ensures that thelimited bandwidth is used to its maximum extent to make sure that themost relevant data items are transmitted first even if the bandwidth isvery low. If a high bandwidth is available when the method switches intotransmission operation mode, the main buffer advantageously provides atleast a limited amount of previously recorded data items that can bereadily transmitted to the ground station. However, the methodadvantageously ensures that any newly created data item is transmittedfirst.

In a preferred embodiment for each of the live buffers a maximum age fordata items to be retained in the live buffer is defined, wherein in thetransmission operation mode a data item is moved from a live buffer to arespective main buffer when an age of the data item exceeds the maximumage defined for the live buffer, wherein any data item that has beenstored in a live buffer before an other data item is moved to the mainbuffer before the other data item.

In other words, for each of the live buffers it is defined how long dataitems will be stored or kept in the live buffer by defining a maximumage of data items that are retained in the buffer. For example, dataitems of the flight data data type may be retained for one minute in therespective live buffer. Data items of the air traffic control messagedata type may be retained for five minutes in the respective livebuffer. If an age of a data item stored in a live buffer exceeds therespective maximum age, i.e., if the data item was created or stored inthe buffer longer ago than the maximum age, the data item is moved tothe respective main buffer. By defining a maximum age for a data itemstored in a live buffer it is ensured that only data items created at arelevant point in time are transmitted. The age of a data item can bedefined from the point in time when the data item was created or fromthe point in time when the data item was stored in a buffer.

If data items are continuously created at predetermined time intervals,i.e., with a fixed frequency, and have a predetermined size, defining amaximum age corresponds to defining a maximum storage capacity for apredetermined number of data items. Cockpit voice recordings may, forexample, be continuously created at predetermined intervals and storedin the form of frames or data items representing 20 ms of recordedsound. A maximum age of cockpit voice recording data items stored in thelive buffer could, for example, be set to 1 minute. Thus, the livebuffer has a maximum storage capacity of 3000 cockpit voice recordingdata items. This is equivalent to stating that the live buffer storesonly data items not older than 1 minute. Thus, in the transmissionoperation mode data items are moved from a live buffer to a respectivemain buffer when the maximum amount of data items that can be stored inthe live buffer has been reached, wherein any data item that has beenstored in a live buffer before an other data item is moved to the mainbuffer before the other data item. The maximum storage capacity of thebuffer may, for example, be limited by the physical storage capacity ofthe memory used for actually storing the data items.

In other words, in this case the buffers have a limited capacity. If themaximum number of data items that can be stored in a buffer has beenreached, the buffer overflows and removes the oldest data item from thebuffer to make space for a new data item. The oldest data item is thedata item stored first in a temporal order in the buffer. However, dataitems from the live buffer are not simply discarded. In the preferredembodiment they are instead moved to the main buffer, i.e., pushed ontothe top of the main buffer. Thus, if the bandwidth of the transmissionlink is temporarily too low to transmit all data items created once thetransmission operation mode has been activated, additional temporarystorage space for data items is provided in the main buffers. If thebandwidth increases while the method is in the transmission operationmode, those data items moved or pushed to the main buffer which arestill stored in the main buffer are available for transmission.

In a preferred embodiment for each data type a separate overflow bufferis provided and associated with the respective data type and for each ofthe main buffers a maximum age for data items to be retained in the mainbuffer is defined. A data item is moved from a main buffer to arespective overflow buffer when an age of the data item exceeds amaximum age defined for the main buffer, wherein any data item that hasbeen stored in a main buffer before an other data item is moved to theoverflow buffer before the other data item. In the transmissionoperation mode any data item stored in a main buffer is transmittedbefore any data item stored in an overflow buffer. Of those data itemsstored in one of the overflow buffers any data item of a data typehaving a higher priority is transmitted before any data item of a datatype having a lower priority. In other words, an additional overflowbuffer provides additional storage space for any data items overflowingfrom the main buffers.

It should be pointed out that in certain embodiments no maximum age isdefined for the live buffers but a maximum age is defined for each ofthe main buffers. In other words, any data item stored in a live bufferis maintained in the live buffer and only data items stored in the mainbuffers are moved to the respective overflow buffers if the age of thedata items stored in the main buffers exceeds a predetermined maximumage. Thus, in this embodiment in the transmission operation mode anydata item of a higher relevance created after the transmission operationmode has been triggered is transmitted before a data item of a lowerrelevance created after the transmission operation mode has beentriggered.

In an exemplary preferred embodiment the method is adapted fortransmitting also data items of an additional data type. The additionaldata type has a different priority than any of the other data typesselected from a range of priorities ranging from a lowest to a highestpriority. For the additional data type a separate overflow buffer isprovided and associated with the additional data type. Data items of theadditional data type are stored in the associated overflow buffer in thetransmission operation mode and in the regular operation mode. Dataitems of the additional data type are treated like data items of any ofthe other data types, i.e., of those data items stored in one of theoverflow buffers including the overflow buffer for an additional datatype any data item of a data type having a higher priority istransmitted before any data item of a data type having a lower priority.An additional data type may, for example, be cockpit images. An overflowbuffer for data items of an additional data type advantageously providesa means of transmitting data items of a lower priority than other dataitems if a high bandwidth should be available. If the method is adaptedfor also transmitting data items of an additional data type, the datatypes for which a live buffer, a main buffer and an overflow buffer areprovided could also be referred to as first data types and theadditional data type for which only an overflow buffer is provided couldalso be referred to as second data type. Consequently, data items of afirst data type could be referred to as first data items and data itemsof a second or additional data type could be referred to as second oradditional data items.

It is further preferred that a payload section of a data packet maycomprise data items of different data types, wherein data items aretransmitted as records, each record comprising a header identifying thedata type of the data item and the length of the record. In other words,data items of different data types can be transmitted in the payloadsection of the same data packet. To this end, the data items of a datatype are packed in records having a header identifying the data type anda payload comprising the data item or data items. This advantageouslyenables the method to completely fill the payload section of a datapacket with data items of different data types if there should not beenough data items from a single data type that have to be transmittedfirst. Thus, the space available in data packet is used optimally.

In a preferred embodiment the method switches from the regular operationmode to the transmission operation mode when a trigger signal isreceived. The trigger signal may, for example, be generated by a methodor a system for determining the risk of an aircraft accident if the riskexceeds a predetermined threshold.

It is further preferred if for at least one of the data types data itemsare stored in frames of a predetermined length in the buffers. For atleast one data type for which data items are stored in frames ofpredetermined size, a plurality of frames can preferably be combined andcompressed to a single compressed frame which is stored in the buffers.For example, if frames of flight data data items are received at abuffer, these frames are first collected in the buffer for apredetermined time span. Once a sufficiently high number of frames hasbeen collected, these frames are combined and compressed into a singlecompressed frame. Thus, if the compressed frames are later transmitted,more relevant data can be transmitted in a shorter time frame, i.e.,with less data packets.

In a second aspect the problem is solved by a transmitter fortransmitting continuously created data items from an aircraft to areceiver. The data items have a plurality of data types and each datatype has been assigned a different priority ranging from a highestpriority to a lowest priority. The transmitter compriseslast-in-first-out buffers for storage of the continuously created dataitems. For each data type a separate live buffer and a separate mainbuffer are provided and associated with the respective data type anddata items of a specific data type are only storable in the associatedbuffers. The transmitter is operable in a regular operation mode and atransmission operation mode. In the regular operation mode thetransmitter is adapted to continuously store continuously created dataitems of the plurality of data types in the associated main buffers. Inthe transmission operation mode the transmitter is adapted to

-   -   continuously store continuously created data items of the        plurality of data types in the associated live buffers,    -   transmit consecutive data packets from the aircraft to a        receiver via a data transmission link, each data packet        comprising a header section and a payload section, and    -   select for each data packet the data to be transmitted in the        payload section from the buffers, wherein any data item stored        in a live buffer is transmitted before any data item stored in a        main buffer, wherein of those data items stored in one of the        live buffers, any data item of a data type having a higher        priority is transmitted before any data item of a data type        having a lower priority, and wherein of those data items stored        in one of the main buffers, any data item of a data type having        a higher priority is transmitted before any data item of a data        type having a lower priority.

In a preferred embodiment for each of the live buffers a maximum age ofdata items retained in the live buffer is defined. The transmitter isadapted to move a data item from a live buffer to a respective mainbuffer in the transmission operation mode when an age of the data itemexceeds the maximum age defined for the live buffer, wherein any dataitem that has been stored in a live buffer before an other data item ismoved to the main buffer before the other data item.

It is further preferred that the transmitter comprises for each datatype a separate overflow buffer associated with the respective data typeand that for each of the main buffers a maximum age for data items to beretained in the main buffer has been defined. The transmitter is adaptedto move a data item from a main buffer to a respective overflow bufferwhen an age of the data item exceeds the maximum age defined for themain buffer, wherein any data item that has been stored in a main bufferbefore an other data item is moved to the overflow buffer before theother data item. In the transmission operation mode any data item storedin a main buffer is transmitted before any data item stored in anoverflow buffer, wherein of those data items stored in one of theoverflow buffers, any data item of a data type having a higher priorityis transmitted before any data item of a data type having a lowerpriority.

In an exemplary preferred embodiment the transmitter is adapted fortransmitting data items of an additional data type. The additional datatype has a different priority than any of the other data types selectedfrom a range of priorities ranging from a lowest to a highest priority.For the additional data type a separate overflow buffer is provided inthe transmitter and associated with the additional data type. Thetransmitter is adapted to store data items of the additional data typein the associated overflow buffer in the transmission operation mode andin the regular operation mode. During transmission data items of theadditional data type are treated like data items of any of the otherdata types, i.e., of those data items stored in one of the overflowbuffers including the overflow buffer associated to the additional datatype any data item of a data type having a higher priority istransmitted before any data item of a data type having a lower prioritystored in an overflow buffer.

In a preferred embodiment a payload section of a data packet maycomprise data items of different data types, wherein data items aretransmitted as records, each record comprising a header identifying thedata type of the data item and the length of the record.

In another preferred embodiment the transmitter is adapted to receive atrigger signal and to switch from the regular operation mode to thetransmission operation mode when the trigger signal has been received.

It is further preferred that for at least one of the data types dataitems are stored in frames of a predetermined length in the buffers. Forat least one data type for which data items are stored in frames ofpredetermined size a plurality of frames can preferably be combined andcompressed to a single compressed frame which is stored in the buffers.

The advantages and exemplary description of the various methodsaccording to the present invention apply vice versa to the embodimentsof a transmitter according to the present invention having structuralfeatures that correspond to the features of the methods.

Finally, in a third aspect the problem is solved by an aircraftcomprising a transmitter according to any of the preceding embodiments.The advantages of the different embodiments of the aircraft correspondto the advantages of the transmitter used therein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, an exemplary embodiment of a method, a transmitter andan aircraft according to the present invention will be explained in moredetail with reference to the schematic drawings, wherein

FIG. 1 shows a flow chart of an exemplary method according to thepresent invention,

FIG. 2 shows an exemplary embodiment of an arrangement of live buffers,main buffers and overflow buffers,

FIG. 3 shows an exemplary embodiment of a live buffer, a main buffer andan overflow buffer,

FIG. 4 shows an exemplary embodiment of a buffer and two data recordsaccording to the present invention,

FIG. 5 shows an exemplary embodiment of a data packet,

FIG. 6 shows an exemplary embodiment of a transmitter according to thepresent invention and

FIG. 7 shows an exemplary embodiment of an aircraft according to thepresent invention comprising an exemplary embodiment of a transmitteraccording to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a flow chart schematically depicting an exemplaryembodiment of a method according to the present invention. The method isprovided for transmitting continuously created data items, such as dataitems stored in a flight recorder of an aircraft, to a ground station.The exemplary embodiment of a method shown in FIG. 1 is adapted fortransmitting data items of the following data types: flight data,cockpit voice recordings and air traffic control messages. To these datatypes may also be referred to as first data types and to data items ofthese data types may also be referred to as first data items. Each ofthe data types has been assigned a different priority selected from arange of priorities extending from a highest priority to a lowestpriority. Air traffic control messages have been assigned the highestpriority, flight data has been assigned the second highest priority andcockpit voice recordings have been assigned the third highest priority.

The method is further adapted for transmitting data items of anadditional or second data type in form of a cockpit images. The dataitems of the additional data type may also be referred to as second dataitems. Further, the additional data type has also been assigned apriority from a range of priorities extending from the highest to alowest priority. The priority assigned to the additional data type isdifferent from the priorities assigned to any of the other data types.In the present example, cockpit images have been assigned the lowest orfourth highest priority.

The exemplary embodiment of a method provides last-in-first-out (LIFO)buffers for the continuously created data items. As can be seen in FIG.2, three different kinds of LIFO buffers are provided: three livebuffers 1 a, 1 b, 1 c, three main buffers 3 a, 3 b, 3 c and fouroverflow buffers 5 a, 5 b, 5 c, 5 d. To improve the ease ofunderstanding, in the following where no reference is made to a specificlive buffer 1 a, 1 b, 1 c, the live buffers will generally be indicatedby reference numeral 1; where no reference is made to a specific mainbuffer 3 a, 3 b, 3 c, the main buffers will generally be indicated byreference numeral 3; and where no reference is made to a specificoverflow buffer 5 a, 5 b, 5 c, 5 d, the overflow buffers will generallybe indicated by reference numeral 5.

For each of the first data types a separate live buffer 1, a separatemain buffer 3 and a separate overflow buffer 5 are provided and assignedto the respective data type. In detail, live buffer 1 a, main buffer 3 aand overflow buffer 5 a are assigned to the air traffic control messagesdata type, live buffer 1 b, main buffer 3 b and overflow buffer 5 b areassigned to the flight data data type and live buffer 1 c, main buffer 3c and overflow buffer 5 c are assigned to the cockpit voice recordingsdata type. For the second data type only an overflow buffer 5 d isprovided and assigned to this data type, i.e., the overflow buffer 5 dis assigned to the cockpit images data type.

The method can operate in two different operation modes. A first orregular operation mode includes a first and a second method step 7, 9and a second or transmission operation mode includes a third, a fourthand a fifth method step 11, 13, 15.

In the regular operation modes any continuously created data item of afirst data type is continuously stored in the main buffer 3 associatedwith the respective data type in the first method step 7. Anycontinuously created data item of the second data type is continuouslystored in the overflow buffer 4 d associated with the second data type.All data items regardless of their type are stored in frames 17 in thebuffers 1, 3, 5. In FIGS. 2, 3 and 4 only a single frame 17 has beenprovided with a reference numeral to keep FIGS. 2, 3 and 4 easy tounderstand.

In the exemplary embodiment of the method shown in FIG. 1 data items arealways stored in the form of frames 17 in the buffers 1, 3, 5. How thecontent of the frames 17 is generated depends on the data type. Forexample, a frame 17 of flight data may comprise uncompressed flight datadata items created over a period of 125 ms. Another frame 17 of flightdata may comprise compressed flight data which has, for example, beengenerated from eighty uncompressed flight data frames 17. Frames 17comprising air traffic control message data items comprise uncompresseddata and frames 17 comprising cockpit voice recordings or cockpit imagesonly comprise compressed recordings or images, respectively.

The second method step 9 checks if a trigger signal has been receivedfrom an external source, for example, from a system determining a riskof an aircraft emergency. If the trigger signal has been received, themethod switches to the transmission operation mode and continues withthe third, fourth and fifth methods steps 11, 13, 15. If no triggersignal has been received, the method continues to operate in the regularoperation mode. It should be noted, that FIG. 1 only shows a schematicrepresentation of the flow of the exemplary embodiment of the method.The first and the second method step 7, 9 do not have to be executed insequence. It is also possible, that the first and the second method step7, 9 are parallel processes. The first method step 7 continuously storescontinuously created data items in the respective buffers 3, 5 and thesecond method step 9 monitors in parallel whether a trigger signal isreceived. If a trigger signal is received, the second method step 9stops the first method step 7 and the method continues with the thirdmethod step 11. The same applies to the third, fourth and fifth methodsteps 11, 13, 15, which are shown in FIG. 1 as sequential method steps.However, method steps 13 and 15 may be implemented as an independentprocess executed in parallel to method step 11.

In the third step 11 data items of a first data type are continuouslystored in the associated live buffers 1, i.e., any air traffic controlmessage data items that are created, are stored in the associated airtraffic control message live buffer 1 a, flight data data items arestored in the associated flight data live buffer 1 b and cockpit voicerecordings data items are stored in the associated cockpit voicerecordings live buffer 1 c. In the same method step 11, any data item ofthe second data type is still stored in the associated overflow buffer 5d.

In the fourth step 13, data items are selected from the buffers 1, 3, 5for transmission in the form of data packets in the fifth step 15. Dataitems are selected from the buffers 1, 3, 5 according to the followingrules: any data item stored in a live buffer 1 has to be transmittedbefore any data item stored in a main buffer 3 and any data item storedin a main buffer 3 has to be transmitted before any data item stored inan overflow buffer 5. Within each buffer category, i.e., live buffer 1,main buffer 3 or overflow buffer 5, every data item of a data typehaving a higher priority has to be transmitted before a data item havinga lower priority. Applied to the exemplary embodiment this means thatfirst any data item of the live buffer 1 a associated with air trafficcontrol messages is transmitted. Next, any data item stored in the livebuffer 1 b associated with flight data is transmitted, followed by anydata item stored in the live buffer 1 c associated with cockpit voicerecordings. If all items from the live buffers 1 have been selected fortransmission, the data items stored in the main buffers 3 are selectedin the same order. Finally, if any data item stored in a main buffer 3has been selected for transmission, data items stored in an overflowbuffer are selected in the order of the priority of the data type. InFIG. 2 the order in which data items are selected from the buffers 1, 3,5 is indicated by the arrow 19.

It should be noted that the buffers 1, 3, 5 are LIFO buffers. Thus,whenever a data item is selected from a buffer 1, 3, 5, the data item isremoved that has been stored last in a temporal order in the buffer 1,3, 5. In other words, the LIFO buffers 1, 3, 5 advantageously add atemporal prioritization to the selection of data items as the LIFObuffers 1, 3, 5 make sure that more recently created data items arealways selected first.

Once the data items for transmission with the next data packet have beenselected in the fourth step, the data items are stored in the payload ofa data packet and transmitted via a data transmission link in the fifthmethod step 15. The data transmission link is a satellite communicationnetwork using the IP protocol for data transmission between aircraft andground station.

It should be noted that every time data items are selected fortransmission with the next data packet, the selection process startsagain at the live buffer 1 a having the highest priority andcontinuously works its way through the buffers 1, 3, 5 selecting dataitems for transmission according to their priority. Thus, it is ensuredthat whenever a new data packet can be transmitted, the most recent andmost highly prioritized data items are transmitted before any data itemhaving arrived earlier or having a lower priority.

Further, providing main buffers 3 advantageously ensures that at thetime the method switches from the regular operation mode to thetransmission operation mode, there is always some data created orrecorded before the transmission operation mode was activated. Inparticular if the method is used to transmit data usually stored in aflight recorder, this data may be helpful for determining the cause ofthe accident as it was captured right before it was detected that thereis a risk of an aircraft emergency and the data, therefore, couldinclude an indication why the transmission operation mode was activated.It should, however, be pointed out that in the method according to thepresent invention any data item of a first data type created after thetransmission operation mode was activated is stored in the liver buffers1 and, therefore, transmitted before the historical data stored in themain buffers 3.

Part of the transmission and selection method steps 13, 15 are shown inmore detail in FIGS. 4 and 5. In FIG. 5, an exemplary embodiment of adata packet 21 is shown in more detail. The data packet 21 comprises aheader section 23 and a payload section 25. The header section 23comprises an IP header 27, a UDP header 29 and an aircraft identifier31. The IP header 27 and the UDP header 29 are part of the transmissionprotocols used for transmitting the data packet 21 via the satellitenetwork. The aircraft identifier 31 is an identifier that unambiguouslyidentifies the aircraft sending the data packet 21. The payload section25 comprises the data items that shall be transmitted packed in severalrecords 33. Each record comprises a record header 35 and a recordpayload 37. The overall maximum allowable size of the data packet 21 isdetermined by the transmission link and the transmission protocol. Eachof the elements 27, 29, 31 of the header section 23 has a predeterminedlength, i.e., comprises a predetermined number of bits. The remainingavailable bits are used for the payload section 25.

The structure of the records 33 and how the records are created from thedata items stored in the buffers 1, 3, 5 will next be described in moredetail with reference to FIG. 4. FIG. 4 shows an arbitrary buffer 39comprising six frames 17 of data items. For the following description itwill be assumed that this buffer 39 is the buffer 39 from which the nextdata items have to be selected according to the rules set out above.From the buffer 39 as many data items are selected as can be fitted inthe payload section 25 of the next data packet 21. The payload section25 may, for example, have enough space left to transmit the data storedin four frames 17. Thus, four frames 17 are selected and added to therecord payload 37 of a first record 33 a. Additionally, headerinformation such as a data type identifier 41, a record payload length43 and a time stamp 45 are added to the record header 35. Once the topfour frames 17 have been selected from the buffer 39, only two frames 17remain in the buffer 39. Assuming that no new frames 17 are added to thebuffer 39 between the selection of data items for two consecutive datapackets 21, the remaining two frames 17 are added to the record payload37 of a second record 33 b. The second record 33 b comprises the samedata type identifier 41 in the record header 35 as the first record 33b, but the record payload length 43 and the time stamp 45 are different.

As can be seen in FIG. 5, if a record 33 comprising data items of asingle data type is not sufficient to fill the entire payload section 25of the data packet 21, records 33 of different data types can beadvantageously be added to the same payload section 25 to maximize thenumber of data items that is transmitted with every data packet 21 andoptimize the use of the available bandwidth.

For each of the buffers a maximum age of data items to be retained inthe buffer has been defined. For flight data data items and cockpitvoice recording data items stored in the respective main buffers 3 b, 3c the maximum age has been defined as five minutes and for data items ofthese data types stored in the live buffers 1 b, 1 c a maximum age hasbeen defined as one minute. For air traffic control messages the maximumage has been defined as two hours for the associated main buffer 3 a and5 minutes for the associated live buffer 1 a. Only data items having anage which is younger, i.e., smaller, than the maximum age are retainedin the respective buffer.

FIG. 3 shows in an exemplary fashion how the live buffer 1 b, the mainbuffer 3 b and the overflow buffer 5 b associated with the flight datadata type are functionally connected. The buffers 1 a, 1 c, 3 a, 3 c, 5a, 5 c associated with the air traffic control messages and the cockpitvoice recordings, respectively, are linked in the same manner. Thebuffers 1 b, 3 b, 5 b are all LIFO buffers having a limited capacity. Asflight data data items are created continuously at a fixed rate, i.e.,with a predetermined frequency, providing buffers of a fixed physicalstorage capacity corresponds to defining a maximum age for data items tobe retained in the buffer. If one of the buffers has reached its maximumcapacity, i.e., the maximum number of frames 17 that can be stored inthe buffer 1 b, 3 b, 5 b has been reached and a newly created frame 17shall be stored in the buffer 1 b, 3 b, 5 b, of those frames 17 storedin the respective buffer 1 b, 3 b, 5 b the frame 47, 49, 51 that hasbeen stored first in a temporal order in the buffer 1 b, 3 b, 5 b isremoved or pushed from the buffer 1 b, 3 b, 5 b. For example, in theregular operation mode new data items are continuously added to the mainbuffer 3 b. As soon as the buffer 3 b has been completely filled withdata items or frames 17, the oldest frame 49 is removed from the mainbuffer 3 b to make space available for the newly added frame 17.

In the exemplary embodiment of the method, frames 47 removed from thelive buffer 1 b are, however, not immediately discarded but moved to themain buffer 3 b. Likewise, any frame 49 removed from the main buffer 3 bis moved to the overflow buffer 5 b. Thus, the main buffer 3 b serves asadditional storage space for data items from the live buffer lb and theoverflow buffer 5 b provides additional storage space for data itemsfrom the main buffer 3 b. This could be particularly advantageous if thebandwidth or data rate available for transmission over the transmissionlink is variable. The bandwidth may, for example, for some time be toolow after the transmission operation mode has been activated to transmitall data items stored in the live buffer 1. At least the live buffers 1c associated with a data type having the lowest priority of the firstdata types will continuously fill up until it overflows and older dataitems are pushed to the respective main buffer 3 c. If after some timethe bandwidth increases, the data items stored in the main buffer 3 care still available and could be transmitted provided that the data rateis high enough. Likewise, if the main buffers 3 are completely filled,the overflow buffers 5 provide additional storage space such that when ahigh data rate should be available, further historic data items can betransmitted. However, by providing main buffers 3 of limited size, it isadvantageously ensured that first the most relevant data items of alldifferent data types are transmitted.

For data items that are continuously created at irregular intervals suchas air traffic control messages the data items are stored with a timestamp and removed from the respective buffer 1 a, 3 a, 5 a when an ageof the data item exceeds the maximum age defined for the respectivebuffer. For example, the maximum age for the live buffer 1 a could beset to five minutes, for the main buffer 3 a to two hours and for theoverflow buffer 5 a to five hours. In other words, the methodcontinuously compares the age of data items stored in the buffers 1 a, 3a, 5 a with maximum age and removes any data item having a maximum ageexceeding the respective maximum age from the buffer. Any data itemremoved from the live buffer 1 a is moved to the main buffer 3 a and anydata item removed from the main buffer 3 a is moved to the overflowbuffer 5 a. Data items removed from the overflow buffer are discarded.

FIG. 6 shows an exemplary embodiment of a transmitter 53. Thetransmitter 53 is adapted to carry out the exemplary embodiment of amethod according to the present invention as described with reference toFIGS. 1 to 5. The transmitter 53 comprises an input 55 which receivesthe continuously created data items, for example, from an aircraft'smain control system. The input 55 further may receive a trigger signalfor switching the transmitter 53 from a regular operation mode to atransmission operation mode and back. Incoming data items are relayed toa distributor 57 which is adapted to distribute the data items dependingon the operation mode and the data type of the data items to one of thebuffers 1, 3, 5 of the transmitter 53. In FIG. 6 the buffers 1, 3, 5 areonly generally indicated and not shown in detail. In particular, thetransmitter 53 comprises a live buffer 1 a, 1 b, 1 c and a main buffer 3a, 3 b, 3 c for each first data type and an overflow buffer 5 a, 5 b, 5c, 5 d for each first and second data type as required for carrying outthe exemplary embodiment of the method which are not shown individuallyin FIG. 6.

The transmitter 53 further comprises a packetizer 59 which selects dataitems or frames 17 from the buffers 1, 3, 5 according to the rules setout above, adds the data items to the record payload 37 of records 33and also adds the necessary header information to the record header 35.Finally, the packetizer also packs the records 33 into the payloadsection 23 of the data packet 21 that is being prepared and adds thenecessary header information to the header section 23. Finally, anoutput 61 transmits the data packets 21 via a data transmission link toa ground station.

With regard to the details of the transmitter 53 reference is made tothe preceding description of the exemplary embodiment of the methodaccording to the present invention. As the transmitter 53 is adapted tocarry out the method as described above, this adds several limitationsto the transmitter 53 that have to be taken into consideration. As thetransmitter 53 is adapted to carry out the method according to thepresent invention, the transmitter 53 shares the advantages of theexemplary embodiment of the method.

Finally, FIG. 7 shows an exemplary embodiment of an aircraft 63according to the present invention. The aircraft 63 comprises atransmitter 53 as shown in FIG. 6. Thus, the above description of thetransmitter 53 fully applies to the aircraft 63. The transmitter's input55 is connected to a main control system 65 of the aircraft 63 and theoutput 61 of the transmitter 53 is connected to a satellite antenna 67for providing a data transmission link.

The aircraft 63 according to the present invention shares the advantagesof the exemplary embodiment of a transmitter 53 and the exemplaryembodiment of the method according to the present invention.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

The invention claimed is:
 1. A method for transmitting continuouslycreated data items from an aircraft to a receiver, wherein the dataitems are of a plurality of data types, wherein each of the plurality ofdata types is assigned a different priority ranging from a highestpriority to a lowest priority, the method comprising: providinglast-in-first-out buffers for storage of the continuously created dataitems, wherein for each data type a separate live buffer and a separatemain buffer are provided and associated with the respective data typeand data items of a specific data type are only stored in the associatedbuffers; in a regular operation mode, continuously storing continuouslycreated data items of the plurality of data types in the associated mainbuffers; in a transmission operation mode, continuously storingcontinuously created data items of the plurality of data types in theassociated live buffers, transmitting consecutive data packets from theaircraft to a receiver via a data transmission link, each data packetcomprising a header section and a payload section, and selecting fromthe buffers, for each data packet, the data to be transmitted in thepayload section, wherein any data item stored in a live buffer istransmitted before any data item stored in a main buffer, wherein of thedata items stored in one of the live buffers, any data item of a datatype having a higher priority is transmitted before any data item of adata type having a lower priority, and wherein of the data items storedin one of the main buffers, any data item of a data type having a higherpriority is transmitted before any data item of a data type having alower priority; and defining, for each of the live buffers, a maximumage for data items to be retained in the live buffer; and in thetransmission operation mode, moving a data item from a live buffer to arespective main buffer when an age of the data item exceeds the maximumage defined for the live buffer, wherein any data item that has beenstored in a live buffer before an other data item is moved to the mainbuffer before the other data item.
 2. The method according to claim 1,wherein a payload section of a data packet may comprise data items ofdifferent data types, wherein data items are transmitted as records,each record comprising a header identifying the data type of the dataitem and the length of the record.
 3. The method according to claim 1,further comprising switching from the regular operation mode to thetransmission operation mode when a trigger signal is received.
 4. Themethod according to claim 1, wherein for at least one of the data typesdata items are stored in frames of a predetermined length in thebuffers.
 5. The method according to claim 4, wherein for at least onedata type for which data items are stored in frames of predeterminedsize, a plurality of frames is combined and compressed to a singlecompressed frame which is stored in the buffers.
 6. A method fortransmitting continuously created data items from an aircraft to areceiver, wherein the data items are of a plurality of data types,wherein each of the plurality of data types is assigned a differentpriority ranging from a highest priority to a lowest priority, themethod comprising: providing last-in-first-out buffers for storage ofthe continuously created data items, wherein for each data type aseparate live buffer and a separate main buffer are provided andassociated with the respective data type and data items of a specificdata type are only stored in the associated buffers; in a regularoperation mode, continuously storing continuously created data items ofthe plurality of data types in the associated main buffers; in atransmission operation mode, continuously storing continuously createddata items of the plurality of data types in the associated livebuffers, transmitting consecutive data packets from the aircraft to areceiver via a data transmission link, each data packet comprising aheader section and a payload section, and selecting from the buffers,for each data packet, the data to be transmitted in the payload section,wherein any data item stored in a live buffer is transmitted before anydata item stored in a main buffer, wherein of the data items stored inone of the live buffers, any data item of a data type having a higherpriority is transmitted before any data item of a data type having alower priority, and wherein of the data items stored in one of the mainbuffers, any data item of a data type having a higher priority istransmitted before any data item of a data type having a lower priority;providing, for each data type, a separate overflow buffer andassociating the separate overflow buffer with the respective data typeand defining, for each of the main buffers, a maximum age for data itemsto be retained in the main buffer; moving a data item from a main bufferto a respective overflow buffer when an age of the data item exceeds themaximum age defined for the main buffer, wherein any data item that hasbeen stored in a main buffer before an other data item is moved to theoverflow buffer before the other data item; and in the transmissionoperation mode, transmitting any data item stored in a main bufferbefore any data item stored in an overflow buffer, wherein of the dataitems stored in one of the overflow buffers any data item of a data typehaving a higher priority is transmitted before any data item of a datatype having a lower priority.
 7. A transmitter for transmittingcontinuously created data items from an aircraft to a receiver, whereinthe data items have a plurality of data types and each data type has adifferent priority ranging from a highest priority to a lowest priority,wherein the transmitter comprises last-in-first-out buffers for storageof the continuously created data items, wherein for each data type aseparate live buffer and a separate main buffer are provided andassociated with the respective data type and data items of a specificdata type are only storable in the associated buffers, wherein thetransmitter is operable in a regular operation mode and a transmissionoperation mode, wherein in the regular operation mode the transmitter isadapted to continuously store continuously created data items of theplurality of data types in the associated main buffers, wherein in thetransmission operation mode the transmitter is adapted to continuouslystore continuously created data items of the plurality of data types inthe associated live buffers, transmit consecutive data packets from theaircraft to a receiver via a data transmission link, each data packetcomprising a header section and a payload section, and select for eachdata packet the data to be transmitted in the payload section from thebuffers, wherein any data item stored in a live buffer is transmittedbefore any data item stored in a main buffer, wherein of those dataitems stored in one of the live buffers, any data item of a data typehaving a higher priority is transmitted before any data item of a datatype having a lower priority, and wherein of those data items stored inone of the main buffers, any data item of a data type having a higherpriority is transmitted before any data item of a data type having alower priority, and wherein for each of the live buffers a maximum agefor data items to be retained in the live buffer is defined, and whereinthe transmitter is adapted to move a data item from a live buffer to arespective main buffer in the transmission operation mode when an age ofthe data item exceeds the maximum age defined for the live buffer,wherein any data item that has been stored in a live buffer before another data item is moved to the main buffer before the other data item.8. The transmitter according to claim 7, wherein a payload section of adata packet may comprise data items of different data types, whereindata items are transmitted as records, each record comprising a headeridentifying the data type of the data item and the length of the record.9. The transmitter according to claim 7, wherein the transmitter isadapted to receive a trigger signal and to switch from the regularoperation mode to the transmission operation mode when the triggersignal has been received.
 10. The transmitter according to claim 7,wherein for at least one of the data types data items are stored inframes of a predetermined length in the buffers.
 11. The transmitteraccording to claim 7, wherein for at least one data type for which dataitems are stored in frames of predetermined size a plurality of framescan be combined and compressed to a single compressed frame which isstored in the buffers.
 12. A transmitter for transmitting continuouslycreated data items from an aircraft to a receiver, wherein the dataitems have a plurality of data types and each data type has a differentpriority ranging from a highest priority to a lowest priority, whereinthe transmitter comprises last-in-first-out buffers for storage of thecontinuously created data items, wherein for each data type a separatelive buffer and a separate main buffer are provided and associated withthe respective data type and data items of a specific data type are onlystorable in the associated buffers, wherein the transmitter is operablein a regular operation mode and a transmission operation mode, whereinin the regular operation mode the transmitter is adapted to continuouslystore continuously created data items of the plurality of data types inthe associated main buffers, wherein in the transmission operation modethe transmitter is adapted to continuously store continuously createddata items of the plurality of data types in the associated livebuffers, transmit consecutive data packets from the aircraft to areceiver via a data transmission link, each data packet comprising aheader section and a payload section, and select for each data packetthe data to be transmitted in the payload section from the buffers,wherein any data item stored in a live buffer is transmitted before anydata item stored in a main buffer, wherein of those data items stored inone of the live buffers, any data item of a data type having a higherpriority is transmitted before any data item of a data type having alower priority, and wherein of those data items stored in one of themain buffers, any data item of a data type having a higher priority istransmitted before any data item of a data type having a lower priority,wherein the transmitter comprises for each data type a separate overflowbuffer associated with the respective data type and wherein for each ofthe main buffers a maximum age for data items to be retained in the mainbuffer has been defined, wherein the transmitter is adapted to move adata item from a main buffer to a respective overflow buffer when an ageof the data item exceeds the maximum age defined for the main buffer,wherein any data item that has been stored in a main buffer before another data item is moved to the overflow buffer before the other dataitem, and wherein in the transmission operation mode any data itemstored in a main buffer is transmitted before any data item stored in anoverflow buffer, wherein of those data items stored in one of theoverflow buffers, any data item of a data type having a higher priorityis transmitted before any data item of a data type having a lowerpriority.
 13. The transmitter according to claim 12, wherein a payloadsection of a data packet may comprise data items of different datatypes, wherein data items are transmitted as records, each recordcomprising a header identifying the data type of the data item and thelength of the record.
 14. The transmitter according to claim 12, whereinthe transmitter is adapted to receive a trigger signal and to switchfrom the regular operation mode to the transmission operation mode whenthe trigger signal has been received.
 15. The transmitter according toclaim 12, wherein for at least one of the data types data items arestored in frames of a predetermined length in the buffers.
 16. Thetransmitter according to claim 12, wherein for at least one data typefor which data items are stored in frames of predetermined size aplurality of frames can be combined and compressed to a singlecompressed frame which is stored in the buffers.
 17. An aircraftcomprising a transmitter for transmitting continuously created dataitems from an aircraft to a receiver, wherein the data items have aplurality of data types and each data type has a different priorityranging from a highest priority to a lowest priority, wherein thetransmitter comprises last-in-first-out buffers for storage of thecontinuously created data items, wherein for each data type a separatelive buffer and a separate main buffer are provided and associated withthe respective data type and data items of a specific data type are onlystorable in the associated buffers, wherein the transmitter is operablein a regular operation mode and a transmission operation mode, whereinin the regular operation mode the transmitter is adapted to continuouslystore continuously created data items of the plurality of data types inthe associated main buffers, wherein in the transmission operation modethe transmitter is adapted to continuously store continuously createddata items of the plurality of data types in the associated livebuffers, transmit consecutive data packets from the aircraft to areceiver via a data transmission link, each data packet comprising aheader section and a payload section, and select for each data packetthe data to be transmitted in the payload section from the buffers,wherein any data item stored in a live buffer is transmitted before anydata item stored in a main buffer, wherein of those data items stored inone of the live buffers, any data item of a data type having a higherpriority is transmitted before any data item of a data type having alower priority, and wherein of those data items stored in one of themain buffers, any data item of a data type having a higher priority istransmitted before any data item of a data type having a lower priorityand defining, for each of the live buffers, a maximum age for data itemsto be retained in the live buffer; and in the transmission operationmode, moving a data item from a live buffer to a respective main bufferwhen an age of the data item exceeds the maximum age defined for thelive buffer, wherein any data item that has been stored in a live bufferbefore an other data item is moved to the main buffer before the otherdata item.